Fiberglassing

Be sure you check whether you have "laminating" or "finish coat" resin. The former is just plain resin, and is used for laying up several layers. Every layer will stick to the previous one very well. The latter contains a wax that floats to the surface of the finished part and, if used in laminating layers, will prevent the layers from bonding, causing part failure. These two resin mixtures are necessary. Polyester resin will harden all the way through except for the very outer surface which is exposed to oxygen. This exposure prevents the resin from hardening and results in an irritating sticky feel to the surface. Using the waxed resin in the final layer allows the wax to float to the surface, insulate the surface from oxygen, allowing it to fully harden. One option is to only use laminating resin, and sand off the outer surface, or prime it, which seals and hardens it. No biggie, don't worry about it, just be careful to not laminate with finishing resin! Another common name for this resin is "sanding resin".